“Kill” systems and catalyst deactivating agents for gas phase polyethylene reactors and for olefin polymerization catalyst systems are known in the art. Prior art thought to be of significance to the claimed invention is discussed below.
U.S. Pat. No. 3,177,184 discloses a method for controlling the polymer production rate of copolymers of ethylene with higher olefins. This patent describes polymerization of ethylene-co-1-butene copolymers using hexavalent chromium oxide catalyst where the ethylene/1-butene content, and thus the copolymer density, can be controlled by controlling the activity level of the catalyst with a deactivator.
U.S. Patent Application Publication Nos. 2004/0230031 A1 and 2004/0151642 A1 both generally disclose methods for deactivating catalysts in polymer streams, e.g., for the purpose of allowing downstream equipment to be repaired or process control problems to be corrected.
U.S. Pat. No. 6,825,292 and European Patent No. EP 1 272 536 both disclose situations in which transitioning between two different types of polyolefin catalysts, particularly when one of those types of catalyst is a “late transition metal” (LTM) catalyst, can cause deactivation of the other type of catalyst.
U.S. Patent Application Publication No. 2004/0253151 A1 and International Publication No. WO 04/109417 both disclose methods for stopping runaway chemical reactions in a reactor by introducing a kill agent into the reactor through actuation of a pressure-sensitive valve, not via measurement of pressure in the reactor and introduction of the kill agent in response to the comparison of the measured pressure to any set pressure.
U.S. Pat. No. 6,365,681 discloses methods for preventing upsets in polymerization reactors by monitoring at least one reaction condition and comparing it to the desired value or normal range for the condition, as projected by a computer model for the variable(s) in the process.
U.S. Pat. Nos. 6,838,531, 6,559,247, 6,262,191, 4,211,863, and 3,269,997 all disclose methods for introduction of catalyst deactivating agents in post-polymerization steps/apparatuses, but not in the polymerization reactor nor in any reaction zone therein, for various reasons, e.g., polymer recovery, catalyst removal, decolorization, and the like.
U.S. Pat. Nos. 5,331,086, 4,634,744, and 3,708,465 each disclose different types of catalyst deactivators, e.g., ketones, metal salts, alcohols, ethers, and the like, and their use in interrupting and/or de-ashing olefin polymerizations.
U.S. Pat. Nos. 5,339,320, 5,270,408, 4,834,947, 4,547,555, 4,326,048, and 4,306,044 all disclose methods for stopping gas phase polymerizations, some under emergency shutdown situations, by introducing a “kill” gas.
The prior art even contains disclosure, i.e., in U.S. Pat. No. 5,237,025, where carbon monoxide is introduced as a reducing gas for a low pore volume silica-supported chromium catalyst as an activating agent, not as a deactivating agent.
Nevertheless, there remains a need, not addressed by the prior art, for ways to control fouling in the reaction zones of slurry-type ethylene-based polymerization reactors using gaseous catalyst poisons to significantly slow or to stop the polymerization to reduce, inhibit, and/or prevent fouling.